Add option to use model hull to steer node/connection generation

[wouterjdb]

Closes #124.

Three new options can be specified in the config:

data_sources:
  concave_hull: True

Which limits new nodes to the volume of the original simulation model.
And,

flownet:
  max_distance: 1000
  max_distance_fraction: 0.15

Which limits the max length of connections after doing the Delaunay triangulation which created the connections.

The resulting FlowNet model for Norne now looks like:

[wouterjdb]

@anders-kiaer I removed mypy from the tests as it didn't like my faking of the config. I actually vote for not using mypy in the tests.

[anders-kiaer]

One suggestion to consider, otherwise LVGTM! 🚀🌻